It's common sense that a teacher deserves a respect from those whom he teaches, but what accessories comes with this respect; for example let's say that a teacher doesn't like a certain hairstyle and then a student comes to the class with this specific hair style, does the teacher have the right to warn the student of coming to the class with that style again, and if the student didn't follow the warning, is it allowed for the teacher to not accept this student in his class? What if it was about clothes instead of hair styles?(or any other things you may think of: tatoos, piercings, ...etc.)

A teacher gives what knowledge and maybe experiences he has to his students, whether the reason for that is that he gets a good salary or because he likes his job and wants to help is irrelevant, since the fact remains that he is giving a lot. But there are teachers whom are just obnoxious, they enjoy just abusing their students(I think this is kind is not that common, but they exist), does that cancel their right to be respected even though they are still giving their students the knowledge they have?

How much authority does a teacher has on his students? How much respect does a teacher deserve? What are the boundaries that limits a teachers' actions? Does a teacher's looks effect how much respect he deserves? Can a bond of friendship be formed with a teacher(this highly depends on one's own definition of friendship, mentioning it is up to whoever wants to contribute to this topic).

A teacher/instructor doesn't have the same authority to his/her students as does the student's parents/guardians. If a teacher/instructor doesn't like a certain hair-style or outfit that his/her student is wearing, they have no right to refuse to teach nor throw that student out. However, if the student was wearing an inappropriate outfit, one that has obscure language written on it or reveals too much skin, then they have the right to tell the student to change and if they don't, they can send the student off to the principal. The principal is the one that runs the school. If any teacher/instructor does not agree with what a student is doing, they have to run it by the principal first. Many teachers/instructors do not do this though. I had a teacher tell me something highly offensive. It was based on her own personal opinion and thus she had no right to say it out loud as she did to me. I however was polite and quietly returned to my seat.

A teacher/instructor deserves utmost respect, as much as you give to your parents, friends, etc. Your future without a proper education from a certified teacher/instructor is gloomy. Teachers/Instructors have their careers because of students like us. They are here to teach and we are here to learn. Without cooperation, we go nowhere. No matter what your teacher/instructor might look like, they still deserve to be treated as an equal. Everyone has their own image. Would you dare make fun of a police-officer who looked different to you? No? Well, it is the same when it comes to your teacher/instructor and as well as anybody else. If a teacher/instructor gives you respect, then you must return it. If they do not show you respect, then prove yourself worthly to them. However, they are some teachers/instructors who are down-right rude and this can be because of many reasons. It's best to still show your respect for them and notify your principal about their behavior. Teachers/Instructors nowadays have to deal with brats rather than students. By the end of the day, they are tired and furious and just want to go home. Teachers/Instructors are also not paid very well and this can add to their daily stress.

A teacher/instructor's role is to teach and guide his/her students. The students, however, shape their own life and image and the teacher/instructor has no legal rights to interfere with that. A bond between a teacher/instructor and student can be made as well. Bonds can be formed through deep-connection and one-on-one support. I had a wonderful friendship with my 4th to 6th grade teacher. He was fun and exciting and my class enjoyed his teachings and company right through until graduation to Junior High School. He was still a teacher though. His lessons were based on the school curriculum, although he pranked us once and made us study a topic that didn't even exist. He also showed his strict side, like when two students got into a fight or when a student was playing a prank and broke an object.

But since the teacher showed his disagreement with a hair-style or an outfit, isn't it out of respect more apropiate for the student not to come to calss with these specific things. An outfit or a hair-style is not that much of an importance that we prefer them over our teachers, by not giving the right to deal with the situation, doesn't that lead us to conclude that we do prefer them over him?
Besides how much skin is too much, it's bad enough and people consider it a normal thing. Hair-style and outfits doesn't have to show inapropiate language, some hair-styles are just stupid, for example what kind of hair-style that makes your head look like a football? or shaving one's head completely except for a line which is made to look like spikes?

Is your opinion when dealing with a university professor?

No, a student is not showing any disrespect by doing so. A student has the right to wear his/her hair and clothing how they choose. So what if their hair is two feet tall? It's dis-respectful for the teacher/instructor to treat their students differently based on how they look. It's bullying to look down on someone based on their appearence. It's inappropriate for a student to wear their pants so they hang down past their knees as well as wear sun-glasses and hats during class. Skimpy outfits are also inappropriate because they violate the school code. No tank tops, no short-shorts, no low-cut jeans, basically no clothing that makes under-garments and private body parts visible. UNLESS what a student is wearing something that is against school rules, then teachers/instructors have to learn to keep their personal thoughts to themselves. Don't get me wrong though, I hate what today's kids are wearing, but if I was their teacher/instructor, I wouldn't say a word.

My opinion is roughly the same when it comes to college/university. These schools for those who graduate high-school, so most students are young adults. They should by now have better sense of etiquette and dress more appropriately. However you will find the odd-balls who still act the same as they did in High School. As long as their don't violate the dress-code, then teachers/instructors/proffesors should keep quiet.

Allow to add a few other questions:
How much influnce does a teacher has on a student's life? or there is no influence at all?

I agree with you all of your points except for one, since I think that knowing that a teacher dislikes a certain style(hair, clothes, ...etc.), but nonetheless following it under the idea that he has no authority on how I look like(though true), is inapropiate, because since I should be appreciating him teaching me and doing what he dislikes is not part of that. Isn't it weird how we always care about the student's right to speak up and go against his teacher if needs to, but when it comes to the teacher, we tell him to shut up since this his work and it's better to do it in silence. You are right teachers shouldn'tbe rude and offensive and have no right to be so, but I think there is anything wrong with saying what they want in a respectful way(In provate with the student or just with the right choice of words in front of the class).